I. Field of the Invention
This invention relates to downhole oil tools utilized to seal or pack-off a casing segment and, in particular, to a downhole tool run on a well string within the casing, the tool including a plurality of retractable slips adapted to permit removal of the tool with a minimum of force and without damaging the casing wall.
II. Description of the Prior Art
Packers and setting tools are widely used in drilling operations to isolate particular segments of the casing or to provide an anchor for other tools. Such devices normally employ one or more sets of slips adapted to engage and "grasp" the casing wall in order to provide solid engagement. Packers normally also include at least one packing element in order to seal off the casing and prevent fluid flow above or below the packer. A tremendous amount of force is applied, either hydraulically or mechanically, to the tool in order to properly set the slips and packer elements. Attempts to overcome this setting force to release the device often times results in damage to the casing wall or the tool itself.
Past known slip assemblies generally comprise a plurality of slip elements circumferentially spaced on the outer periphery of the tool. The slip elements include outer serrations adapted to engage the casing wall. A longitudinally movable slip cone disposed beneath the slip assembly is utilized to wedge the slip elements outwardly against the casing wall. Interacting sloped surfaces on the cone and the leading edge of the slip elements gradually moves the slips towards the casing wall. In order to prevent lateral and longitudinal movement of the slips, each element is disposed within a slip window formed as part of an outer sleeve. The slip window and the edges of the slips are provided with square surfaces to ensure that the elements travel radially outward. However, because of the square abutment of the slip window with the slip element when an attempt is made to retract the slips, an unacceptable amount of force is required. Accordingly, in many packers and setting tools only one set of slips, below the packing elements, is normally utilized to initially anchor the tool.